Polyacetal resin is used in diverse fields as an engineering plastic due to its excellent physical properties, such as mechanical, electrical and chemical properties (e.g., chemical and heat resistances). However, the identification of new and/or specific end-use applications for polyacetal resins often requires further property alterations and/or enhancements. One such property enhancement/alteration that has been identified for polyacetal resins is greater resistance against various bacteria and/or fungi.
In general, plastics materials are superior in terms of corrosion resistance as compared to wood, natural fibers and metals and are therefore widely used in numerous end-use applications. However, damage to plastics materials due to bacteria and/or fungi sometimes causes a problem even though plastic materials are less susceptible to bacteria and/or fungi growth as compared to water-absorbing materials such as wood and natural fibers. Although bacteria and/or fungi growth on plastics materials rarely cause any serious change in the materials' properties, bacteria and/or fungi growth can be odiferous thereby causing the surrounding environment to be less pleasant, as well as causing the appearance of the plastics materials to deteriorate. In addition, parts formed of a plastics material on which bacteria and/or fungi have grown may stain other materials with which they come into contact.
It is therefore highly desirable to employ antibacterial and/or antifungal plastics materials to form parts which are to be used in high humidity environments (e.g., residential kitchens, lavatories, bathrooms, and production/packaging chambers used in the food industry) as well as "clean room" production environments (e.g., equipment, walls, ceilings and floors of an electronics production line). More particularly, parts formed of antibacterial and/or antifungal plastics materials are especially desirable in machine parts and other components that are subjected to warm and moist conditions during use, such as air conditioners, food processing equipment, refuse disposers and humidifiers.
Various antibacterial and antifungal agents have recently been developed in order to prevent deterioration of plastic products due to bacteria and fungi. In general, a successful antibacterial and antifungal agent to be added to plastics materials must exhibit the following characteristics: (1) be harmless to man and animals; (2) exhibit no leaching or bleeding of the agent when exposed to water; (3) will not affect the physiochemical properties of the resin; (4) prevent corrosion of metals; and (4) be odorless. It is also preferable from the viewpoint of prolonged effectiveness that the agent be physically incorporated (blended) into the plastics material. However, known antibacterial and antifungal agents do not always satisfy the above-noted requirements and/or can be physically incorporated into plastics materials.
For example. N-(fluorodichloromethylthio)-phthalimide and N,N-dimethyl-N'-phenyl-N'-fluorodichloromethylthiosulfamide, which are known antibacterial and antifungal agents for plastics and coatings materials have relatively low decomposition temperatures (i.e., 180.degree. C. and 120.degree. C., respectively) and thus cannot be incorporated into plastics materials which are to be processed by molding at significantly higher temperatures. On the other hand, another known agent, i.e., 10,10'-oxybisphenoxyarsine, has a characteristic odor which makes its handling and use unpleasant. Thiobendazoles have also been identified as potential bacterial and antifungal agents for plastics materials but are problematic due to their propensity to "bleed" from the plastics materials causing the surfaces to become quite sticky. Some conventional antifungal agents can undergo color changes when exposed to light and thus cannot be incorporated into white molded plastics products without seriously affecting the products' appearance.
The addition of conventional antibacterial and/or antifungal agents to polyacetal resins is particularly problematic. That is, polyacetal resins are sometimes rendered chemically unstable by addition of additives due to the inherent characteristics of the same. Thus, it is typically difficult to add a number of known antibacterial and antifungal agents such as those cited above to polyacetal resins.
What has been needed in this art, therefore, is a polyacetal resin composition which exhibits antibacterial and/or antifungal effects by blending into the polyacetal an antibacterial and/or antifungal agent having high temperature stability. It is towards fulfilling such a need that the present invention is directed.
Broadly, the present invention is embodied in novel polyacetal resin compositions which include an effective amount of an antibacterial and/or antifungal agent which contains a specific metal ion which is selected from silver, copper and zinc ions. More specifically, the antibacterial and/or antifungal polyacetal resin compositions of this invention will comprise 100 parts by weight of a polyacetal base resin, and between about 0.1 to 5 parts by weight of at least one antibacterial and/or antifungal agent which contains a metal ion selected from silver, copper and zinc ions.
Further aspects and advantages of the present invention will become apparent after careful consideration is given to the following detailed description of the same.